U.S. patent application number 14/422523 was filed with the patent office on 2015-08-20 for charging device for secondary battery and charging method for secondary battery.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. The applicant listed for this patent is NISSAN MOTOR CO., LTD.. Invention is credited to Tsutomu Soga, Atsushi Takano.
Application Number | 20150236541 14/422523 |
Document ID | / |
Family ID | 50149765 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150236541 |
Kind Code |
A1 |
Takano; Atsushi ; et
al. |
August 20, 2015 |
CHARGING DEVICE FOR SECONDARY BATTERY AND CHARGING METHOD FOR
SECONDARY BATTERY
Abstract
A charging device includes charging power detection unit and
full charge determination unit. The charging device further
includes charging control unit adapted to repeatedly execute a
additional charging control until the number of times of the full
charge determination reaches a predetermined full charge
determination count. The charging device further includes unit
adapted to detect the temperature of the secondary battery, and
full charge determination count setting unit adapted to set a
larger full charge determination count as the temperature decreases
at least based on the temperature of the secondary battery when the
full charge determination is made.
Inventors: |
Takano; Atsushi;
(Sagamihara-shi, JP) ; Soga; Tsutomu;
(Machida-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSAN MOTOR CO., LTD. |
Yokohama-shi, Kanagawa |
|
JP |
|
|
Assignee: |
NISSAN MOTOR CO., LTD.
Yokohama-shi, Kanagawa
JP
|
Family ID: |
50149765 |
Appl. No.: |
14/422523 |
Filed: |
July 10, 2013 |
PCT Filed: |
July 10, 2013 |
PCT NO: |
PCT/JP2013/068823 |
371 Date: |
February 19, 2015 |
Current U.S.
Class: |
320/107 ;
320/137 |
Current CPC
Class: |
G01K 13/00 20130101;
H01M 10/443 20130101; H01M 10/486 20130101; H02J 7/0047 20130101;
H02J 7/0091 20130101; G01R 31/382 20190101; H01M 10/0525 20130101;
H02J 7/0049 20200101; H02J 7/00 20130101; Y02E 60/10 20130101 |
International
Class: |
H02J 7/00 20060101
H02J007/00; G01K 13/00 20060101 G01K013/00; G01R 31/36 20060101
G01R031/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2012 |
JP |
2012-181793 |
Claims
1. A charging device for secondary battery, comprising: a charging
power supply capable of outputting power for charging a secondary
battery: a charging power detection unit adapted to detect power to
be charged to the secondary battery by the charging power supply; a
full charge determination unit adapted to make a full charge
determination if chargeable power calculated based on a detection
value of the charging power detection unit becomes equal to or less
than predetermined power set in advance; a charging control unit
adapted to execute a charging control of supplying power to the
secondary battery from the charging power supply until the full
charge determination is made, stopping the supply of power to the
secondary battery from the charging power supply when the full
charge determination is made, resuming the supply of power upon the
elapse of a predetermined time after the supply of power is stopped
and continuing the supply of power until the full charge
determination is made again until the number of times of the full
charge determination reaches a full charge determination count
which is a predetermined count; a temperature detection unit
adapted to detect the temperature of the secondary battery; and a
full charge determination count setting unit adapted to set the
full charge determination count at least based on the temperature
detected by the temperature detection unit when the full charge
determination is made, wherein the full charge determination count
setting unit setting a larger full charge determination count as
the temperature detected by the temperature detection unit
decreases.
2. The charging device for secondary battery according to claim 1,
further comprising: a stop time setting unit adapted to set a time
for stopping the supply of power at least based on the temperature
detected by the temperature detection unit when the full charge
determination is made, wherein the stop time setting unit sets a
longer stop time for stopping the supply of power as the
temperature detected by the temperature detection unit
decreases.
3. The charging device for secondary battery according to claim 2,
further comprising: a stop time correction unit adapted to
reductively correct the stop time set by the stop time setting unit
every time the full charge determination is made.
4. The charging device for secondary battery according to claim 3,
wherein: the stop time correction unit holds the stop time when the
full charge determination count reaches the predetermined count
thereafter once the full charge determination count reaches the
predetermined count.
5. A charging method for secondary battery, comprising: a charging
power detection step of detecting power to be charged to a
secondary battery by a charging power supply capable of outputting
power for charging the secondary battery; a full charge
determination step of making a full charge determination when
chargeable power calculated based on a detection value of the
charging power detection step becomes equal to or less than
predetermined power set in advance: a charging control step of
repeatedly executing a charging control of supplying power to the
secondary battery from the charging power supply until the full
charge determination is made, stopping the supply of power to the
secondary battery from the charging power supply when the full
charge determination is made, resuming the supply of power upon the
elapse of a predetermined time after the supply of power is stopped
and continuing the supply of power until the full charge
determination is made again until the number of times of the full
charge determination from the start of charging reaches a
predetermined count; further comprising: a temperature detection
step of detecting the temperature of the secondary battery; and a
full charge determination count setting step of setting a larger
predetermined count as the temperature detected by the temperature
detection step decreases at least based on the temperature detected
by the temperature detection step when the full charge
determination is made.
6. A charging device for secondary battery, comprising: a charging
power supply capable of outputting power for charging a secondary
battery; charging power detection means for detecting power to be
charged to the secondary battery by the charging power supply; full
charge determination means for making a full charge determination
if chargeable power calculated based on a detection value of the
charging power detection means becomes equal to or less than
predetermined power set in advance; charging control means for
repeatedly executing a charging control of supplying power to the
secondary battery from the charging power supply until the full
charge determination is made, stopping the supply of power to the
secondary battery from the charging power supply when the full
charge determination is made, resuming the supply of power upon the
elapse of a predetermined time after the supply of power is stopped
and continuing the supply of power until the full charge
determination is made again until the number of times of the full
charge determination reaches a full charge determination count
which is a predetermined count; temperature detection means for
detecting the temperature of the secondary battery; and full charge
determination count setting means for setting the full charge
determination count at least based on the temperature detected by
the temperature detection means when the full charge determination
is made, wherein the full charge determination count setting means
setting a larger full charge determination count as the temperature
detected by the temperature detection means decreases.
Description
TECHNICAL FIELD
[0001] This invention relates to a charging control for secondary
battery.
BACKGROUND ART
[0002] A known charging device for secondary battery performs
so-called additional charging by detecting a fully charged state of
a secondary battery based on the temperature and voltage of the
secondary battery, stopping charging when the fully charged state
is detected and resuming charging after the elapse of a
predetermined time after the stop. JP2003-143770A discloses a
charging device for performing such additional charging, which
device detects a peak voltage at the time of a full charge
detection and increases a repeat count of additional charging as
the peak voltage decreases.
SUMMARY OF INVENTION
[0003] However, if the repeat count of additional charging is set
as in the above literature, there is a problem that an actually
charged state of the secondary battery cannot be brought closer to
the fully charged state in some cases.
[0004] Accordingly, the present invention aims to set an
appropriate repeat count of additional charging at which a
secondary battery can be brought to a state closer to a fully
charged state and the execution of useless additional charging can
be avoided.
BRIEF DESCRIPTION OF DRAWINGS
[0005] FIG. 1 is a configuration diagram of a charging system of a
first embodiment.
[0006] FIG. 2 is a flow chart of a charging control routine
according to the first embodiment.
[0007] FIG. 3 is a full charge determination count table.
[0008] FIG. 4 is a time chart in the case of executing a charging
control.
[0009] FIG. 5 is a time chart showing effects by the first
embodiment.
[0010] FIG. 6 is a configuration diagram of a charging system of a
second embodiment.
[0011] FIG. 7 is a flow chart of a charging control routine
according to the second embodiment.
[0012] FIG. 8 is a stop time map.
[0013] FIG. 9 is a time chart showing effects by the second
embodiment.
[0014] FIG. 10 is a correction coefficient table for charge stop
time correction.
DESCRIPTION OF EMBODIMENTS
[0015] Hereinafter, embodiments of this invention are described
with reference to the accompanying drawings.
First Embodiment
[0016] FIG. 1 is a configuration diagram of a charging system of an
embodiment of the present invention.
[0017] The charging system includes a battery 3, a charger 2 as a
charging power supply for supply charging power to the battery 3
and a controller 1 for controlling the charger 2. The charging
system further includes a current sensor 4 as charging power
detection means for detecting a charging current supplied from the
charger 2 to the battery 3, a voltage sensor 5 as charging power
detection means for detecting a battery voltage and a temperature
sensor 6 as temperature detection means for detecting the
temperature of the battery 3.
[0018] The controller 1 calculates power to be charged to the
battery 3 from the charger 2 based on detection values of the
current sensor 4 and the voltage sensor 5, and the controller 1
sends a charging power command based on the calculated charging
power to the charger 2. Further, the controller 1 also reads a
detection value of the temperature sensor 6. The internal
configuration of the controller 1 is described later.
[0019] The charger 2 supplies charging power based on the charging
power command from the controller 1 to the battery 3.
[0020] The battery 3 is a secondary battery such as a lithium-ion
battery used, for example, as a power source for driving a drive
motor of an electric vehicle, and charged by the charging power
supplied from the charger 2.
[0021] The detection values of the current sensor 4, the voltage
sensor 5 and the temperature sensor 6 are read into the controller
1.
[0022] Next, the internal configuration of the controller 1 is
described. It should be noted that an operation content in each
constituent unit is described with reference to a flow chart of
FIG. 2.
[0023] The controller 1 includes a chargeable power calculating
unit 11, a charging power commanding unit 10 as full charge
determination means and charging control means, a timer 12, a
counter 14 and a full charge determination count setting unit 13 as
full charge determination count setting means.
[0024] The chargeable power calculating unit 11 reads the detection
values of the current sensor 4 and the voltage sensor 5 and
calculates chargeable power based on these. The chargeable power is
a maximum value of power chargeable to the battery 3 without
promoting the degradation of the battery 3, and power receivable by
the battery 3. This chargeable power is generally also referred to
as inputtable power, maximum chargeable power or maximum inputtable
power in addition to the chargeable power.
[0025] The charging power commanding unit 10 sends a charging power
command based on the chargeable power calculated in the chargeable
power calculating unit 11 to the charger 2. Further, the charging
power commanding unit 10 determines a fully charged state and stops
charging, i.e. sets the charging power command at zero (kW) when
the chargeable power calculated in the chargeable power calculating
unit 11 becomes equal to or less than predetermined power set in
advance. Further, when the charging power commanding unit 10
determines a fully charged state, the charging power commanding
unit 10 sends a command for causing the full charge determination
count setting unit 13 to set a full charge determination count
(hereinafter, referred to as a full charge determination count
setting command) as a predetermined count. The charging power
commanding unit 10 reads a count value of the timer 12 to be
described later after sending a stop time setting command. When the
count value becomes zero, the charging power commanding unit 10
will resume the sending of the charging power command based on the
chargeable power to the charger 2, thereby performing so-called
additional charging. The timer 12 has a stop time after the full
charge determination set in advance and starts counting down
(process of reducing the count value at every predetermined time).
A minimum value of the count value is zero.
[0026] The full charge determination count setting unit 13
calculates a full charge determination count corresponding to a
battery temperature and sets the calculated full charge
determination count in the counter 14 upon receiving the full
charge determination count setting command from the charging power
commanding unit 10. It should be noted that, although described in
detail later, the full charge determination count corresponding to
the battery temperature increases as the battery temperature
decreases.
[0027] The counter 14 increments a counter value every time the
full charge determination is made due to additional charging. This
counter value is a value which is initially zero and incremented
every time the full charge determination is made due to additional
charging, and an integrated value of the number of times of the
full charge determination from the start of additional charging.
The charging power commanding unit 10 finishes the charging control
when the counter value of the counter 14 reaches the set full
charge determination count.
[0028] FIG. 2 is a flow chart of a charging control routine
executed by the controller 1.
[0029] In a Step S10, the controller 1 calculates the chargeable
power. More specifically, the chargeable power is calculated based
on the detection value of the current sensor 4 and that of the
voltage sensor 5 in the chargeable power calculating unit 11 and
sent to the charging power commanding unit 10, and the charging
power commanding unit 10 sends the charging power command to the
charger 2.
[0030] Here, an example of a chargeable power calculation method is
descried. First, a deviation between a full charging voltage set in
advance and the detection value of the voltage sensor 5, i.e. a
voltage increase margin .DELTA.V up to the full charging voltage is
calculated. Subsequently, a current increase margin .DELTA.I until
the voltage of the battery 3 reaches the full charging voltage is
calculated using the voltage increase margin .DELTA.V and a
resistance R of the battery 3 measured in advance. A power increase
margin until the full charging voltage is reached, i.e. the
chargeable power can be calculated from the voltage increase margin
.DELTA.V and the current increase margin .DELTA.I.
[0031] In a Step S20, the controller 1 determines in the charging
power commanding unit 10 whether or not the fully charged state has
been reached. Specifically, the fully charged state is deter mined
if the chargeable power becomes equal to or less than predetermined
power determined in advance (hereinafter, this determination is
referred to as the "full charge determination"). The predetermined
power may be set at zero [kW] from the purpose of determination in
this step, but there is a possibility that the chargeable power
does not decrease to zero and the fully charged state is not
determined due to detection errors of the sensors 4, 5 and the
like. Accordingly, such a value substantially close to zero [kW]
that the fully charged state can be determined even in the presence
of errors of the sensors 4, 5 is set.
[0032] As a result of the determination, the controller 1 executes
a processing of a Step S30 if the full charge determination is
made, whereas the controller 1 executes a processing of the Step
S10 again unless the full charge determination is made.
[0033] The full charge determination is only a determination that
the chargeable power has become equal to or less than the
predetermined power, but not a determination that the battery 3 has
actually reached the fully charged state (ion adsorption amount of
a negative electrode is maximized).
[0034] In the Step S30, the controller 1 determines whether or not
the full charge determination of the Step S20 is the first full
charge determination. Specifically, the controller 1 determines
whether or not the counter value of the counter 14 is zero. If the
counter value of the counter 14 is zero, the controller 1
determines that the full charge determination of the Step S20 is
not the full charge determination in additional charging and
executes a processing of a Step S50. On the other hand, if the
counter value of the counter 14 is larger than zero, the controller
1 determines that the full charge determination of the Step S20 is
the full charge determination in additional charging and executes a
processing of a Step S40.
[0035] In the Step S40, the controller 1 sets a full charge
determination count N until the end of the charging control after
the first full charge determination. Specifically, the full charge
determination count N set here is the number of times of performing
additional charging. The number of times of performing additional
charging can also be set at N by setting a full charge
determination count N+1 as a full charge determination count from
the start to the end of the charging control. In the following
description, the full charge determination count N is set as the
number of times of performing additional charging until the end of
the charging control after the first full charge determination.
[0036] The full charge determination count setting unit 13 reads
the detection value of the temperature sensor 6, determines the
full charge determination count N by referring to a full charge
determination count table stored in advance, sets the determined
count (full charge determination count N) and counts the number of
times of determining the full charge. The full charge determination
count table is such that the count increases as the battery
temperature decreases, for example, as shown in FIG. 3. This is
based on a characteristic that it takes a longer time to resolve
polarization as the battery temperature decreases. For example, in
the case of a lithium-ion battery, polarization results from a
density difference caused by the dispersion of lithium ions which
are dispersion substances. The viscosity of an electrolytic
solution increases and it takes a longer time to resolve
polarization as the battery temperature decreases. Thus, if
additional charging is performed without polarization being
sufficiently resolved while charging is stopped, the fully charged
state is immediately reached on the surface. Accordingly, it is
possible to bring the charged state closer to a true fully charged
state by setting a larger full charge determination count as the
battery temperature decreases.
[0037] It should be noted that a stop time map is not limited to
that of FIG. 3 if a condition of setting a larger stop count as the
battery temperature decreases is satisfied. For example, a
temperature region may be divided into a plurality of sections and
the stop count may be set for each section.
[0038] In the Step S50, the controller 1 determines whether or not
the number of times of determining the full charge (i.e. counter
value of the counter 14) has become N, which is the full charge
determination count set in the Step S30, or larger. If the number
of times of determining the full charge is N or larger, the counter
value of the counter 14 is reset to zero and a charging power
command value is set at zero [kW] in the charging power commanding
unit 10 and sent to the charger 2, thereby finishing the charging
control.
[0039] In a Step S60, the controller 1 increments the value of the
counter that counts the number of times of determining the full
charge. The counter increments the counter value every time the
full charge determination is made in the Step S20 until the counter
value is determined to be not smaller than a specified count in
Step S50.
[0040] In a Step S70, the controller 1 sets the charging power
command value at zero [kW] in the charging power commanding unit 10
and sends it to the charger 2, thereby stopping charging.
[0041] In a Step S80, the controller 1 determines whether or not a
charging stop time has elapsed in the charging power commanding
unit 10. The charge stop time is a time set in advance and, for
example, about several minutes.
[0042] As described above, a larger charge stop count (which is the
full charge determination count N and also written as the charge
stop count below) as the battery temperature at the time of the
full charge determination decreases, and additional charging is
repeatedly performed until the full charge determination count
reaches the charge stop count, thereby bringing the charged state
of the battery 3 closer to the true fully charged state.
[0043] FIG. 4 is a time chart in the case of executing the above
charging control.
[0044] When charging is started, the battery voltage gradually
increases. It should be noted that the chargeable power is a
constant value until timing T1. This is because, although larger
chargeable power is calculated in operation, it is limited by P1
which is an upper limit of supply capability of the charger 2.
[0045] The chargeable power starts decreasing from timing T1, at
which the battery voltage approaches the full charging voltage,
when the calculated chargeable power falls below P1 as the upper
limit of supply capability of the charger 2, and the full charge
determination is made to temporarily stop charging at timing T2 at
which the chargeable power becomes equal to or less than P2 which
is a predetermined value set for the full charge determination.
From timing T3 after the elapse of the charge stop time, additional
charging is started. Thereafter, until the full charge
determination count reaches the charge stop count N, charging is
similarly repeatedly stopped and resumed.
[0046] FIG. 5 is a time chart of the amount of power charged to the
battery 3. As a comparative example, a case is also shown where the
full charge determination count is constant (2 times) regardless of
the battery temperature. In both the present embodiment and the
comparative example, the charge stop time is a predetermined time
set in advance.
[0047] It should be noted that the amount of power in the true
fully charged state (a state close to the true fully charged state
is meant and, hereinafter, merely referred to as the true fully
charged state) is P24 [kWh]. Further, the battery temperature is,
for example, near -25.degree. C. Thus, in the present embodiment,
the full charge determination count is set at 3 times based on the
table of FIG. 3. That is, an additional charging count in the
present embodiment is 3 times, whereas that in the comparative
example is 2 times.
[0048] In both the present embodiment and the comparative example,
the first full charge determination is made at timing T21 at which
the amount of power reaches P21 [kWh]. In the present embodiment,
the full charge determination count N is set here.
[0049] In both the present embodiment and the comparative example,
charging is resumed at timing T22 reached upon the elapse of the
charge stop time, the full charge determination is made and a full
charge determination counter is set at 1 at timing T23 at which the
amount of power reaches P22 [kWh]. Then, charging is resumed at
timing T24 reached upon the elapse of the charge stop time, and the
full charge determination is made and the full charge determination
counter is set at 2 at timing T25 at which the amount of power
reaches P23 [kWh].
[0050] In the comparative example in which the additional charging
count is set at 2 times, charging is finished here. Thus, charging
is finished at the amount of power P23 less than the amount of
power P24 [kWh] in the true fully charged state. Contrary to this,
since the additional charging count is 3 times in the present
embodiment, charging is resumed at timing T26 reached upon the
elapse of the charge stop time and performed until timing T27 at
which the third full charge determination is made. In this way, the
amount of charging power reaches P24 [kWh] and the true fully
charged state can be set.
[0051] It should be noted that if the additional charging count of
the comparative example set in advance is 3 times, the true fully
charged state can be set as in the present embodiment. However, if
the battery temperature is, for example, 10 [.degree. C.] or 20
[.degree. C.], additional charging is uselessly performed even
after the true fully charged state is already reached. Contrary to
this, the additional charging count is reduced as the battery
temperature increases in the present embodiment in which the
additional charging count is set according to the battery
temperature, such useless additional charging is not performed.
[0052] As described above, the following effects are achieved
according to the present embodiment.
[0053] Due to the occurrence of polarization, a secondary battery
may be set in a fully charged state on the surface even if it is in
a chargeable state. Accordingly, the resolution of polarization is
waited by stopping charging for a predetermined time after the
fully charged state is detected, and then additional charging is
performed. However, if the temperature of the secondary battery
decreases, polarization is resolved at a slower rate and the amount
of power chargeable by one additional charging is reduced. Thus, it
may not be possible to charge sufficient power if a repeat count
set according to a peak voltage is used, for example, as disclosed
in the above patent literature 1. On the other hand, if the repeat
count is so set that the fully charged state can be set even if the
temperature of the secondary battery is low, additional charging is
uselessly performed when the temperature of the secondary battery
is a normal temperature.
[0054] According to the present embodiment, the full charge
determination count setting unit 13 is provided which sets the full
charge determination count N at least based on the battery
temperature when the full charge determination is made, and sets a
larger full charge determination count N as the battery temperature
decreases. Since the repeat count of additional charging can be set
at an appropriate count according to the battery temperature in
this way, the true fully charged state can be set and the execution
of useless additional charging can be avoided.
Second Embodiment
[0055] In a second embodiment, the charge stop time after the full
charge determination is set according to the battery temperature at
the time of the full charge determination in addition to the
control of the first embodiment.
[0056] FIG. 6 is a configuration diagram of a charging system of
the second embodiment. Basically, the second embodiment is similar
to the first embodiment, but differs therefrom in that a full
charge determination count setting unit 13 calculates not only the
full charge determination count, but also the charge stop time
after the full charge determination and the set charge stop time is
set in a timer 12.
[0057] FIG. 7 is a flow chart of a charging control routine
executed by a controller 1 in the second embodiment. The controller
1 sets the full charge determination count N according to the
battery temperature in the first embodiment, but also sets the
charge stop time according to the battery temperature in addition
to the full charge determination count N in the second embodiment.
Here, points of difference from the first embodiment are
described.
[0058] Steps S110, S120 and S130 are not described since being
similar to Steps S10, S20 and S30 of FIG. 2.
[0059] In a Step S140, the controller 1 sets the full charge
determination count N according to the battery temperature by a
procedure similar to that in the Step S40 of FIG. 2 and further
sets the charge stop time according to the battery temperature.
[0060] The full charge determination count N set here is similar to
that of the first embodiment in that it increases as the battery
temperature decreases, but becomes smaller than in the first
embodiment as the battery temperature decreases. This is described
later.
[0061] The controller 1 determines the charge stop time by reading
a detection value of a temperature sensor 6 and referring to a stop
time map stored in advance. The controller 1 sets the determined
setting time in the timer 12 and starts the countdown of the timer
12. The stop time map is configured to set a longer stop time as
the battery temperature decreases, for example, as shown in FIG. 8.
This is based on a characteristic that it takes a longer time to
resolve polarization as the battery temperature decreases. For
example, in the case of a lithium-ion battery, polarization results
from a density difference caused by the dispersion of lithium ions
which are dispersion substances and the viscosity of an
electrolytic solution increases and it takes a longer time to
resolve polarization as the battery temperature decreases. Thus,
polarization is sufficiently resolved until charging is resumed by
setting a longer charge stop time as the battery temperature
decreases.
[0062] Further, by performing additional charging in a state where
polarization is sufficiently resolved, the amount of charging power
by additional charging is increased per additional charging. Thus,
an additional charging count required until a true full charge is
reached can be reduced. However, since a shorter time is required
to resolve polarization in a state where the battery temperature is
high than in a state where the battery temperature is low, an
effect of resolving polarization by extending the charge stop time
is small. Therefore, the additional charging count can be reduced
by setting the charge stop time according to the battery
temperature only in a region where the battery temperature is
low.
[0063] It should be noted that the stop time map is not limited to
that of FIG. 8 if a condition of setting a longer stop time as the
battery temperature decreases is satisfied. For example, a
temperature region may be divided into a plurality of sections and
the stop time may be set for each section.
[0064] Further, once the full charge determination count and the
charge stop time are set after the first full charge determination,
the set values are maintained until the charging control is
finished.
[0065] Steps S150 to S180 are not described since being similar to
Steps S50 to S80 of FIG. 2.
[0066] As described above, additional charging is repeatedly
performed by setting a larger full charge determination count and a
longer charge stop time as the battery temperature at the time of
the full charge determination decreases, thereby bringing the
charged state of a battery 3 closer to the true fully charged
state.
[0067] FIG. 9 is a time chart of the amount of power charged to the
battery 3. As a comparative example, a case is also shown where the
control of the first embodiment is executed. It should be noted
that the amount of power in the true fully charged state is P35
[kWh]. Further, the battery temperature is near -25.degree. C. as
in FIG. 5, and it is assumed that the full charge determination
count is set at 3 times in the first embodiment and at 2 times in
the second embodiment based on the table of FIG. 3.
[0068] A chart of the first embodiment is similar to that of FIG.
5, the first full charge determination is made at timing T31 and
the true fully charged state is reached at timing T41 by repeating
additional charging three times thereafter.
[0069] Contrary to this, in the second embodiment, charging is
stopped until timing T33 later than timing T32 after the first full
charge determination is made at timing T31. This causes additional
charging to be performed in a state where the resolution of
polarization is advanced, and the amount of power reaches P33 [kWh]
larger than the amount of power P32 at the end of the first
additional charging in the first embodiment when the full charge
determination is made by the first additional charging. Then, at
timing T39 at which the second additional charging is finished, the
power of amount reaches P35 [kWh], i.e. the true fully charged
state is reached.
[0070] As described above, a time until the true fully charged
state is reached can be shortened by setting a longer charge stop
time after the full charge determination as the battery temperature
decreases in addition to setting a larger additional charging count
as the battery temperature decreases.
[0071] It should be noted that, in the above description, the full
charge determination count and the charge stop time set after the
first full charge determination are maintained until the end of the
control. However, to further increase the efficiency of the
charging control, the charge stop time may be corrected every time
the full charge determination is made. For example, in additional
charging, a charging current is smaller than that before the full
charge determination and a density difference of the dispersion
substances by polarization is less likely to be generated since the
battery voltage is close to the full charging voltage. That is, the
battery voltage is less likely to drop while charging is stopped
after the full charge determination. Thus, the influence of
polarization becomes smaller as the full charge determination count
increases and the charge stop time for waiting for the resolution
of polarization can be shortened. Accordingly, it is prevented to
set a charge stop time longer than necessary by multiplying the
charge stop time set according to the battery temperature by a
correction coefficient .alpha., which is a value not larger than 1
and becomes smaller as the full charge determination count
increases, to shorten the charge stop time as the full charge
determination count increases.
[0072] For example, the correction coefficient .alpha. is set by
reading a table set in advance as shown in FIG. 10. It should be
noted that, in FIG. 10, the correction coefficient .alpha. is
constant in the fourth and subsequent full charge determinations
although it becomes gradually smaller every time the full charge
determination is made in the first to fourth full charge
determinations. The correction coefficient .alpha. is constant in
the fourth and subsequent full charge determinations because the
influence of polarization hardly changes.
[0073] Further, the battery temperature may be read every time the
full charge determination is made and the full charge determination
count may be readjusted based on the battery temperature. An
appropriate full charge determination count corresponding to an
increase of the battery temperature during additional charging can
be set.
[0074] By the above, the following effects are obtained in the
present embodiment in addition to effects similar to those of the
first embodiment.
[0075] The stop time setting unit 13 is further provided which sets
the charge stop time at least based on the battery temperature at
the time of the full charge determination, a longer charge stop
time is set as the battery temperature decreases. Thus, the
resolution of polarization is advanced until the start of
additional charging and additional charging can be more efficiently
performed.
[0076] Since the charge stop time is reductively corrected every
time the full charge determination is made, the charge stop time
corresponding to a degree of resolution of polarization can be set
and additional charging can be more efficiently performed.
[0077] In the above reductive correction, the stop time when the
full charge determination count reaches a predetermined count is
kept thereafter once the full charge determination count reaches
the predetermined count. Thus, an appropriate charge stop time can
be set also after the aforementioned influence of polarization no
longer changes.
[0078] Embodiments of this invention were described above, but the
above embodiments are merely examples of applications of this
invention, and the technical scope of this invention is not limited
to the specific constitutions of the above embodiments.
[0079] This application claims priority based on Japanese Patent
Application No. 2012-181793 filed with the Japan Patent Office on
Aug. 20, 2012, the entire contents of which are incorporated into
this specification.
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